1. Field of the Invention
This specification relates generally to network systems and methods for transmitting image data from one node to another through the IEEE1394 aerial bus, and in particular, to such network systems and methods capable of transmitting image data in a broadcast like communication manner in order to perform tandem image formation within the network.
2. Discussion of the Related Art
The IEEE1394 was approved in 1995 as the IEEE 1394-1955 standard and is well known as a serial bus standard for use in digital data communication. P1394a and P1394b specifying the IEEE1394 have been similarly approved. A serial bus meeting the IEEE1394 standard is generally called an IEEE 1394 serial bus.
FIG. 1 illustrates a typical system meeting such an IEEE1394 standard. Specifically, various electronic instruments such as PCs, TVs, etc., meeting the IEEE1394 standard are employed as nodes 11. An IEEE serial bus 12 is formed from a cable meeting the IEEE1394 standard and serially connects the various electronic instruments. Connection terminals of the cable are each formed from a connecter having four, six, or more pins.
FIG. 2 illustrates a protocol meeting the IEEE1394 standard. The protocol of the IEEE1394 standard is formed, as is conventional, from a physical layer 21, a link layer 22, a transaction layer 23, and a serial bus control 25 that controls these three layers. Both of the physical and link layers 21 and 22 are formed from hard wares. Both the transaction layer 23 and serial bus 25 are formed from prescribed firm wares. An application layer 24 is provided as an upper link layer of the above-mentioned three layers.
The physical layer 21 executes bus configuration when bus rest, such as bus initialization, tree recognition, self-recognition, etc., takes place. The physical layer 21 also executes bus acquiring when packet transfer such as arbitration, etc., takes place. The link layer 22 executes packet transfer such as isochronous transfer, asynchronous transfer, asynchronous stream, etc., as described below. The transaction layer 23 executes an instructing operation such as “Read”, “Write”, “Lock”, etc.
Since it has not been standardized by the IEEE1394-1995 standard, the application layer 24 is standardized by a SBP2 or SBP3 standard. The, SBP2 standard standardizes, for example, an operation relating to an initiator (i.e., a node forwarding an instruction) and a target (i.e., a node receiving the instruction). The serial bus control 25 is formed from a bus manager, an isochronous resource manager, and a node controller. The bus manager executes bus management such as topology map offering, speed map offering, etc. The isochronous resource manager executes isochronous resource management such as isochronous band allocation, channel number allocation, etc., as described infra. The node controller executes node control.
Various advantages of the EEEE1394 standard are exemplified as follows: The first is assurance of a real time performance enabled by isochronous transfer. The second is Hot-Plug-In realizing connection and disconnection while keeping power supply turned ON. The third is Plug and Play enabling automatic execution of bus configuration in response to the connection and disconnection.
In such an environment, the IEEE1394 serial bus has recently received attention as a serial bus that is used in order to connect instruments to each other in a digital copier, a digital copier to a peripheral such as an optional unit, and digital copiers to each other. For example, tandem copying and similar operations, in which image data from a digital copier is transmitted in order to simultaneously form images in other plural units of digital copiers, are attempted using the IEEE1394 serial bus as discussed in Japanese Patent Application Laid Open Nos. 2000-295382 and 2001-16382, which are herein incorporated by reference in their entirety.
Further, tandem printing and similar operations, in which image data from a scanner is transmitted in order to simultaneously form images in plural units of printers, are attempted using the IEEE1394 serial bus. For the purpose of overall comprehension of these operations, formation of images simultaneously performed by the plural units of image forming apparatuses will be referred to as tandem image formation.
Referring now to FIG. 3, a conventional tandem copier is briefly described. As shown, three units of digital copiers 31A, 31B, and 31C are serially connected via two IEEE1394 serial buses 32A and 32B.
Tandem copying is performed on condition that the digital copier 31A serves as an image transmission apparatus and remaining digital copiers 31B and 31C serve as image forming apparatuses. Specifically, the digital copier 31A obtains image data with its scanner unit and forms an image on a sheet or the like with its image formation unit in accordance with the image data. The digital copier 31A subsequently transmits the image data to the other digital copiers 31B and 31C. These digital copiers 31B and 31C then form images in accordance with the image data on sheets with their image forming units, respectively. As understood from the above, the former image formation relates to single unit copying, and the latter image formations relates to tandem copying.
In such tandem copying, since the digital copier 31A necessarily transmits image data to the digital copiers 31B and 31C after separately sending a communication inquiry signal and receiving a communication possible signal to and from each of the digital copiers 31B and 31C, a quantity of image data passing through the serial bus and a time period required in transmitting the image data amount to those for two units, when, for example, N number of units of digital copiers execute the tandem copying, the quantity of data and the time period amount to those for (N−1) units.
In such a way, increase in a unit number of digital copiers performing tandem copying results in large consumption of a common resource of a serial bus band and increasing in a transmission time period. Especially, when a quantity of image data is large in relation to the bus bandwidth (i.e., a data transfer speed), this may disable image data transfer to catch up an operation of the digital copier. Stated differently, a capacity of a serial bus may become a bottleneck when a digital copier performs tandem copying. This may take place not only in tandem copying, but also in other types of tandem image formation.